1. Field of the Invention
The present invention relates to a communication system that is suitable for application to a system including a device to perform an input or output compliant with the HDMI (High-Definition Multimedia Interface) standard, which is a digital video-audio I/O interface standard, and a transmitting-receiving device used in the communication system.
2. Description of the Related Art
The HDMI standard has been developed as an interface standard to mutually communicate non-compressed digital video data and the like between a plurality of video devices. Based on the HDMI standard, the video data can be transmitted individually in one pixel unit as primary color data of each color. In the HDMI standard, audio data is also transmitted during a blanking period of the video data using a transmission line of the video data. The primary color data for transmission include primary color data of red, green and blue (R-data, G-data and B-data). It is also possible to transmit the primary color data of subtractive color mixture of cyan, magenta and yellow.
One pixel data of each color is basically transmitted per eight-bit unit. A synchronization signal such as a horizontal synchronization signal and a vertical synchronization signal is transmitted when each signal is provided. In addition, a transmission line for pixel clock of the video data and a transmission line for control data are also provided. Since the data transmission is configured such that the non-compressed digital video data is conducted based on a pixel unit as described, a high definition video and the like can be transmitted with copyright protection.
A device that generates a video signal source, such as a disk reproducing apparatus, is generally connected with a display device (such as a monitor receiver and a television receiver) in connecting the plurality of video devices using the transmission line (HDMI cable) of the HDMI standard. A device for outputting the video data and the like to the transmission line of the HDMI standard indicates a source device (output device) and a device for inputting the video data and the like through the transmission line of the HDMI standard indicates a sink device (input device).
Details of the HDMI standard are described in International Patent Publication No. WO2002/078336.
In the HDMI standard, a line capable of bi-directionally transmitting control data, a CEC (Consumer Electronics Control) line, is separately provided from the transmission line of the video data, in order to perform control between the source device and the sink device. Thus, it is possible to control an counterpart device using this CEC line. A control example using the CEC line is described in Unexamined Japanese Patent Application No. 2004-208290.
Since a control method using this CEC line is an optional in the HDMI standard, compatibility is not secured among devices of respective manufacturers corresponding to the HDMI standard. In the control method using the CEC line of the HDMI standard, a feature that should be followed minimally on the standard is prescribed as “Mandatory” (mandatory feature), but a control feature other than the mandatory feature is “Option” and there is no compatibility among respective manufacturers as long as the optional feature is used.
Therefore, if the plurality of video devices are connected by using the transmission line of the HDMI standard, it may be unidentifiable which command of the CEC standard the connected device complies with, and hence it may be unclear whether or not the connected device complies with a command until a key operation is performed to send the command and the connected devices are actually operated based on that key operation. If the key operation corresponding to a non-compliant feature is performed, it may not be easy for the user to know that the device is non-compliance since non-compliance device can be identified only when no operation is performed after the reception of the command.
According to an embodiment of the present invention, a compliant control feature of an counterpart device can be easily identified in a case that a plurality of devices are connected by using such transmission line.